An e-mail service usually acts as a hub of a user's data, messages, communication, and even as a user's information/knowledge base. The information/knowledge base in e-mails could be very large, such that it is usually impractical for the user to know relevant contents among a large amount of e-mails in a situation where such content may be needed, especially if the user subscribes to one or more highly-active mailing lists or large online forums. There is content and/or contact information in the user's e-mail inbox that is not cared by or even read by the user at the time of reception, but which may turn out to be greatly helpful later on at a proper time when the user actually needs the valuable information or critical contact.